Reactions

Alkyl halides are fairly stable compounds, like the alkanes that they are similar to in structure.

Combustion

Like the alkanes, they will burn. Unlike the alkanes, even under the most ideal conditions, the products of combustion are not just CO₂ and H₂O. The halogen will also combine with oxygen to form a halogen oxide which, in the presence of moisture, becomes an acid (like those we studied last term).

Substitution

Alkyl halides can be formed or synthesized by substitution reactions between alkanes and halogens. They can also react by substitution reactions as well.

As is shown here (and in example 24 in your workbook), methane can react with chlorine by a substitution reaction to form chloromethane, thus creating an alkyl halide.

Chloromethane can also react with chlorine by a substitution reaction to make dichloromethane.

By the way, I picked a one-carbon compound as an example so that I would not have to worry about which hydrogen atom would be replaced. In a compound with more carbon atoms replacing different hydrogen atoms could result in the formation of a variety of different compounds.

H             H
|             |
H-C-H + Cl₂ Ž H-C-Cl + HCl
|             |
H             H

H              H
|              |
H-C-Cl + Cl₂ Ž H-C-Cl + HCl
|              |
H              Cl

Flame Test

Another reaction can be used to distinguish alkyl halides from other types of compounds such as alkanes. Because alkanes and alkyl halides physically look like one another (most of them are clear, colorless liquids), we have to use chemical tests to distinguish between them. This reaction involves the way that alkyl halides react with copper. The raction between hot copper wire and an alkyl halide will form a copper halide that gives a green flame when put back in a Bunsen burner flame. You will become familiar with this reaction when you do Part II of the experiment for this lesson.

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E-mail instructor: Eden Francis

Clackamas Community College
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